Battle of the Bulge ... German spies behind Allied lines

From World War II: An Interactive Package of Media and Text (1989, pp. 320-321):

A feature of the attack was the activities of the so-called 150th Panzer Brigade, a unit of some 2,000 English-speaking German commandos who knew American service slang and customs.

Under Colonel Otto Skorzeny, using captured American Jeeps and wearing American combat jackets over their German uniforms, the Germans advanced far ahead of the main force, cutting telephone wires, turning sign posts, setting up false red minefield indicators and creating as much confusion as possible. Each was under orders, if captured, to tell their captors that thousands of Germans were loose in American uniforms, driving Jeeps.

The success of the first group was outstanding -- forty Jeeps got through the American lines to commit their sabotage, and all but eight got back again. Those that were captured duly carried out their orders and spread rumors of a vast force of Germans in U.S. uniform -- with the result that huge traffic jams developed on the narrow roads through the forest as Jeeps were stopped and checked. Hundreds of Ameican soldiers who failed to prove their American origin by answering check questions correctly were arrested. Many a GI had cause to reflect in the cooler that a little more attention to school day lessons about the height of the Empire State Building and the content of the Gettysburg Address might have saved him a lot of bother.

Later groups of ... saboteurs were less successful although one man captured on the 19th launched a fresh rumor of an attempt on Eisenhower's life which caused a rash of extra security precautions that did much to slow the Supreme Commander's progress for days.

Since the activities of the 150th Panzer Brigade were entirely contrary to the Geneva Convention, the Americans began summarily to try and shoot the men captured in U.S. uniform, and this ended their incursions.[my emphasis]

More World War II history should be taught in public schools.